The design and development of semiconductor Integrated Circuits (ICs) tends to be rather expensive and, in fact, many hours of engineering talent are required to develop the complex structures, processes and manufacturing techniques involved in making modern semiconductor devices and ICs. Indeed, semiconductor ICs over the years have become more complex and therefore the effort involved in achieving a successful design has become very expensive. Many man-hours of highly skilled professional time are required at a considerable expense to design and develop a modem integrated circuit.
Others, in order to avoid not only the expense involved in the design and development of integrated circuits, but also to avoid the significant time involved in bringing a new integrated circuit design to the market place, resort to reverse engineering practices for existing integrated circuits to take apart, probe, and otherwise examine these existing ICs to try to determine the physical structures and methods used to make the integrated circuit for subsequent copying. This reverse engineering, which typically relies primarily on obtaining planar optical images of a circuit, in essence tries to bypass the typical product development cycles and expenses involved in producing integrated circuits.
Since the reverse engineer is trying to go for a “free ride” on the efforts of others, various approaches have been developed to try to thwart the reverse engineer, particularly in the field of semiconductor integrated circuits. See, for example, U.S. Pat. No. 4,583,011 wherein the device is given a depletion implant that is virtually invisible to a reverse engineer.
Integrated circuits typically comprise a large number of active devices, typically in the form of transistors, diodes, and the like, which are electrically connected by the means of interconnects. The interconnects are often provided by metallic structures which are formed on various levels within an integrated circuit device. Since these metallic structures etch away in the presence of an appropriate etchant at a different rate compared to the other structures found in a semiconductor device (such as semiconducting material, insulating material, and the like), the reverse engineer can discover the presence and the structure of metallic conductors used to interconnect the active devices in an integrated circuit by putting the needed time and energy into the reverse engineering task. However, since this time and energy is less than that required to design a new IC, reverse engineering has its followers. Indeed, the reverse engineer's object is to make a working, slavish copy of the original IC, caring little about how the original IC was designed. The reverse engineer does not seem to be deterred by the fact that in many countries existing ICs are legally protected against copying by some form of mask works protection. As such, in order to protect the considerable investment made in new IC designs, other or additional steps are needed to deter such slavish copying.